This invention relates to a chuck and more specifically, to the workholding top jaw of a chuck.
A chuck consists of a body with inserted workholding jaws that slide radially in slots on the chuck and are actuated by various mechanisms such as screws, scrolls, levers and cams, alone or in a variety of combinations. Typically, a workpiece will be secured to a chuck by radially positioning the workholding jaws against the outer surface of the workpiece. As an example, FIG. 1, which is prior art, shows a three-jaw chuck having a chuck body 10, which may be formed of a one-piece steel casting, mounted upon the spindle (not shown) of a machine for securing a workpiece 15. Three chuck jaws 20 on the chuck body 10 are operated upon to effect simultaneous gripping action on the workpiece 15. The chuck body 10, chuck jaws 20 and operating components are of an entirely conventional nature and will not be described in detail. The construction and operation of the mechanism for jaw positioning is also well understood by those skilled in the art and further elaboration will not be provided.
Throughout this discussion reference will be made to one of what will be multiple chuck jaws 20 and their associated components. For that reason only one set of jaws 20 and associated components will be discussed in detail with the understanding that such a discussion is applicable to the other chuck jaws.
In order to secure the workpiece 15 the chuck jaws 20 are radially urged along a radial axis 21 against the workpiece 15 such that the workpiece 15 is securely held in place about a longitudinal axis 22, which is the chuck 10 centerline. In typical chucking operations the force exerted on the workpiece 15 by the chuck jaws 20 is substantial and may be high enough to deform the surface of the workpiece 15. By design, the material of the chuck jaws is typically softer than the material of the associated workpiece 15. In this manner any damage that may occur would occur to the chuck jaws 20. For this reason each chuck jaw 20 is provided with an additional removeable jaw, known as a top jaw 25.
A top jaw 25 may be secured to a receiving face 27 of each chuck jaw 20, thereby alleviating the need to replace a chuck jaw 20 in favor of replacing the top jaw 25 which may be relatively easily removed or secured to the chuck jaws 20 using a means for securing such as threaded bolts. In this manner the chuck 10 may be easily maintained by simply replacing each top jaw 25 when it becomes damaged.
A critical consideration when utilizing chucks is the proper positioning of the workpiece 15. Often times the workpiece 15 must be positioned with tolerances in the thousandths of inches. The positioning of a top jaw 25 about a workpiece, even when properly mounted to the chuck jaw 20, requires adjustment. This is typically accomplished by mounting the top jaw 25 upon the chuck jaw 20 and boring the gripping surface 30 of each top jaw 25 to provide a desired level of concentricity among the gripping surfaces 30 of the top jaws 25. However, after these top jaws 25 are used and become damaged they must then be replaced and a new set of top jaws 25 must be mounted and once again bored to the proper concentricity.
Boring these top jaws 25 can be a time consuming operation. Furthermore, each jaw 25 has limited material allowed for reboring and once that limit is reached, the jaws 25 have to be replaced with new ones and the boring process repeated.
An object of this invention is to alleviate the need for a boring operation each time a new set of top jaws is mounted upon the chuck jaws.
A further object of this invention is to provide a top jaw configuration that alleviates this need for boring but at the same time is compatible with existing chuck bodies.
Still another object of this invention is to provide an arrangement in which the top jaws may be manually adjusted to provide the concentricity necessary to properly support a workpiece.
Still another object of this invention is to provide a design modification to existing chucks which could be simple and inexpensive to implement while still providing the manual adjustment for concentricity necessary to alleviate the need for reboring.